Neuropsychiatric symptoms and past manganese exposure in a ferro-alloy plant

Neurological and neurobehavioral effects of welders in Egypt exposed to manganese containing welding fumes

PURPOSE

Welders are more likely to develop neurobehavioral disorders because of their exposure to neurotoxic metals such as manganese. This study aimed to measure the neurobehavioral performance of welders occupationally exposed to manganese at welding enterprises and its relationship with the workplace environment.

METHODS

It is a comparative cross-sectional study carried out on 130 welders working at 50 welding enterprises in Menoufia governorate, Egypt, compared to 130 non-occupationally exposed controls.

RESULTS

It was found that the environments of the studied welding enterprises had levels of respirable dust, manganese, and total welding fumes that exceeded internationally permissible limits. In addition, the mean blood manganese levels were significantly higher among welders (4.16 ± 0.61) than the controls (1.72 ± 0.41). Welders had a significantly higher prevalence of neurological manifestations and lower performance of neurobehavioral tests. Lower neurobehavioral performance among welders was significantly correlated with increased work duration and blood levels in some tests.

CONCLUSION

To lessen the fumes in the breathing zone of workers, it is therefore strongly recommended to regularly wear high-quality personal protective equipment, especially masks, and to ensure proper ventilation.

Vitamin E protects dopaminergic neurons against manganese-induced neurotoxicity through stimulation of CHRM1 and KCNJ4

BACKGROUND

Manganese (Mn) overexposure can induce neurotoxicity and lead to manganism. Vitamin E (Vit E) has neuroprotective effects by acting as an ROS scavenger, preventing mitochondrial dysfunction and neuronal apoptosis. However, the effects of Vit E on Mn-induced nigrostriatal system lesions remains unknown.

OBJECTIVES

We aim to investigate whether Vit E has protective effects on Mn-induced nigrostriatal system lesions and mRNA expression profiles in the SN of mice.

METHODS

Sixty 8-week-old C57BL/6 male mice were randomly divided into the Control, MnCl2, MnCl2 +Vit E, and Vit E group. Twenty-four hours after the last injection, the behaviour test was performed. The numbers of dopaminergic neurons in Substantia nigra (SN), the contents of dopamine and its metabolite levels in striatium, and the morphology of mitochondria and nuclei in the dopaminergic neurons in SN were detected by immunofluorescence staining, high-performance liquid chromatography, and transmission electron microscopy. Transcriptome analysis was used to analyze the signaling pathways and RT-PCR was used to verify the mRNA levels.

RESULTS

Vit E ameliorates behavioral disorders and attenuates the loss of nigral dopaminergic neurons in the Mn-induced mouse model. In addition, Vit E antagonized Mn-induced toxicity by restoring mitochondrial function. The results of transcriptome sequencing and RTPCR show that the protective effect of Vit E was related to the upregulation of CHRM1 and KCNJ4 mRNA in the SN.

CONCLUSIONS

Vit E has neuroprotective effects on Mn-induced neurodegeneration in the nigrostriatal system. This effect may be related to the upregulation of CHRM1 and KCNJ4 mRNA stimulated by Vit E in the SN.

Trace Elements Levels in Major Depressive Disorder-Evaluation of Potential Threats and Possible Therapeutic Approaches

The multifactorial etiology of major depressive disorder (MDD) includes biological, environmental, genetic, and psychological aspects. Recently, there has been an increasing interest in metallomic studies in psychiatry, aiming to evaluate the role of chosen trace elements in the MDD etiology as well as the progression of symptoms. This narrative review aims to summarize the available literature on the relationship between the concentration of chosen elements in the serum of patients with MDD and the onset and progression of this psychiatric condition. The authors reviewed PubMed, Web of Science, and Scopus databases searching for elements that had been investigated so far and further evaluated them in this paper. Ultimately, 15 elements were evaluated, namely, zinc, magnesium, selenium, iron, copper, aluminium, cadmium, lead, mercury, arsenic, calcium, manganese, chromium, nickel, and phosphorus. The association between metallomic studies and psychiatry has been developing dynamically recently. According to the results of current research, metallomics might act as a potential screening tool for patients with MDD while at the same time providing an assessment of the severity of symptoms. Either deficiencies or excessive amounts of chosen elements might be associated with the progression of depressive symptoms or even the onset of the disease among people predisposed to MDD.

Biomarkers for occupational manganese exposure

Long-term inhalation exposure to manganese (Mn) metal or its inorganic compounds can result in manganism or subclinical neurofunctional deficits. Studies have described affected workers in Mn dioxide mining, Mn-containing ore crushing and milling facilities, manufacturing of dry-cell batteries, Mn steel and alloy production plants, and in welders. The objective of this study was to critically review existing evidence on the reliability of potential biomarkers of Mn exposure, specifically the relationship between inhalation exposure to Mn particulates in different occupational settings and Mn concentrations in blood and other biological fluids and tissues, with a particular focus on whole blood as a potentially useful medium for measuring internal tissue dose. We also examined available evidence on the relationship between Mn levels in blood and adverse clinical and subclinical neurotoxic outcomes. Three bibliographic databases were searched for relevant studies and identified references were screened by two independent reviewers. Of the 6338 unique references identified, 76 articles were retained for data abstraction. Findings indicate that the relationships between Mn in blood and both external Mn exposure indices and neurofunctional impairments are limited and inconsistent. Different sources of exposure to Mn compounds, heterogeneity in the methodological approaches, and inadequate reporting of essential information limited direct comparison of the reported findings. Among the Mn-exposure biomarkers considered in this review - including biomarkers in blood, plasma, serum, erythrocytes, urine, bone, toenails, fingernails, hair, saliva - biomarkers in whole blood may provide to be most useful in Mn biomonitoring and risk assessment.

Analytical method using SEM-EDS for metal elements present in particulate matter generated from stainless steel flux-cored arc welding process

Welding fumes (WFs) can cause occupational pneumonoconiosis and other diseases in workers. WFs have complex chemical composition and morphology depending on the welding conditions. The WF surface is a key factor affecting those diseases. The objective of this study was to establish an analytical method focused on characterizing individual WFs and welding slags (WSs) formed during CO₂ arc welding processes for knowledge acquisition of risk assessment. Especially, the characterization was focused on the elemental distributions near the surfaces obtained using fluxing agents and size of the WFs. WFs were collected using personal samplers. After welding, WS was also collected. The fluxing elemental distribution (e.g., Bi) near the surfaces WS and WFs were analyzed through scanning electron microscopy and energy-dispersive X-ray spectroscopy. As a result, some of the micron-sized spherical particles (SPs) grew by incorporating nanosized primary particles composed of other metal species. The fluxing agents formed elemental distribution patterns on the SP surface. Bi were dotted in an agglomerate. Mn amount in WS depends on Mn amount in the WFs. These results obtained through the analysis of both the WS and WF surface as well as the particle sizes will facilitate the establishment of exposure assessment models.

Depression and anxiety in a manganese-exposed community

OBJECTIVE

To characterize the association between residential environmental manganese (Mn) exposure and depression and anxiety, given prior associations among occupationally-exposed workers.

METHODS

We administered the Beck Depression Inventory (BDI) and the State-Trait Anxiety Inventory (STAI) to 697 study participants in their preferred languages. These participants represented a population-based sample of residents aged ≥40 from two predominantly Black African communities in Gauteng province, South Africa: 605 in Meyerton, adjacent to a large Mn smelter, and 92 in Ethembalethu, a comparable non-exposed community. We investigated the associations between community (Meyerton vs. Ethembalethu) and severity of depression and anxiety, using linear regression, adjusting for age and sex. To document community-level differences in Mn exposure, we measured airborne PM_2.5-Mn.

RESULTS

Meyerton residents had BDI scores 5.63 points (95 % CI 3.07, 8.20) higher than Ethembalethu residents, with all questions contributing to this significant difference. STAI-state scores were marginally higher in Meyerton than Ethembalethu residents [2.12 (95 % CI -0.17, 4.41)], whereas STAI-trait scores were more similar between the communities [1.26 (95 % CI -0.82, 3.35)]. Mean PM_2.5-Mn concentration was 203 ng/m³ at a long-term fixed site in Meyerton and 10 ng/m³ in Ethembalethu.

CONCLUSION

Residence near Mn emission sources may be associated with greater depression symptomatology, and possibly current, but not lifetime, anxiety.

Blood manganese levels during pregnancy and postpartum depression: A cohort study among women in Mexico

BACKGROUND

Occupational studies have shown an association between elevated Mn exposure and depressive symptoms. Blood Mn (BMn) naturally rises during pregnancy due to mobilization from tissues, suggesting it could contribute to pregnancy and postpartum depressive symptoms.

OBJECTIVES

To assess the association between BMn levels during pregnancy and postpartum depression (PPD), creating opportunities for possible future interventions.

METHODS

We studied 561 women from the reproductive longitudinal Programming Research in Obesity, Growth, Environment, and Social Stressors (PROGRESS) cohort in Mexico City. BMn was measured at the 2nd and 3rd trimesters, as well as delivery. The Edinburgh Postnatal Depression Scale (EPDS) was used to assess PPD symptoms at 12-months postpartum. We used a generalized linear model assuming a Poisson distribution to assess the association between BMn levels and PPD, with adjustments for age, stress and depressive symptoms during pregnancy, education, socioeconomic status, and contemporaneous blood lead levels.

RESULTS

The mean ± standard deviation (SD) EPDS score at 12-months postpartum was 6.51 ± 5.65, and 17.11% of women met the criteria for possible PPD (score ≥ 13). In adjusted models, BMn during the 3rd trimester (β: 0.13, 95% CI: 0.04-0.21) and BMn levels averaged at the 2nd and 3rd trimester (β: 0.14, 95% CI: 0.02-0.26) had a positive association with EPDS scores at 12 months postpartum. BMn at the 2nd trimester (β: 0.07, 95% CI: -0.09-0.22) and delivery (β: 0.03, 95% CI: -0.04-0.10) had a non-significant positive association with EPDS scores at 12-months postpartum. Stress and depressive symptoms during pregnancy was associated with higher EPDS scores at 12-months postpartum in all of the adjusted models but were only significant when either BMn during 3rd trimester or BMn averaged across 2nd and 3rd trimester was assessed as the exposure.

DISCUSSION

Our results demonstrate that elevated BMn levels during pregnancy predict PPD symptoms and could be a potential pathway for intervention and prevention of PPD.

Ethanol Exacerbates Manganese-Induced Neurobehavioral Deficits, Striatal Oxidative Stress, and Apoptosis Via Regulation of p53, Caspase-3, and Bax/Bcl-2 Ratio-Dependent Pathway

This study investigated the effects of ethanol (EtOH) on manganese (Mn)-induced striatal toxicity in rat by evaluating the neurobehavioral changes, biochemical and molecular events in rats exposed to Mn alone at 30 mg/kg, or their combination with EtOH at 1.25- and 5-g/kg body weight for 35 consecutive days. Locomotive and exploratory profiles were assessed using a video tracking software (ANY-Maze software) during a 5-min trial in a novel environment. Subsequently, acetylcholinesterase (AChE) activity, oxidative stress markers, histological morphology, and expression of apoptotic proteins (p53 and Bax and caspase-3) and anti-apoptotic protein (Bcl-2) were assessed in the striatum. Results showed that Mn, EtOH, and their combination induced locomotor and motor deficits. Track plot analysis indicated that EtOH exacerbated the Mn-induced reduction in exploratory profiles of exposed rats. Similarly, exposure of rats to Mn, EtOH, or combination of Mn and EtOH resulted in decreased activities of anti-oxidant enzymes, diminished level of reduced glutathione, downregulated Bcl-2 expression, increased AChE activity, enhanced hydrogen peroxide and lipid peroxidation levels, and upregulated expressions of p53, Bax, and caspase-3. Moreover, potentiation of Mn-induced striatal toxicity by EtOH co-exposure was dose dependent. Taken together, it seems that EtOH exacerbates Mn-induced neurobehavioral deficits, oxidative stress, and apoptosis induction via the regulation of p53, caspase-3, and Bax/Bcl-2 ratio-dependent pathway in rat striatum.

Toenail manganese as biomarker of drinking water exposure: a reliability study from a US pregnancy cohort

Manganese (Mn) is an essential nutrient; however, overexposure can be neurotoxic. Recent evidence suggests that exposure to Mn from drinking water could be neurotoxic; however, research is hampered by the lack of consensus on a reliable biomarker of Mn exposure. Naturally high concentrations of Mn can occur in groundwater, particularly for private, unregulated water systems. This study aimed to investigate the association between exposure to Mn from drinking water with a relatively low Mn content (median of 2.9 μg/L; range, undetectable-8,340 μg/L) and Mn in toenails from women collected at two time points: during and after pregnancy. Mn concentrations in the paired toenail samples gathered during the second to third trimester of pregnancy and 2 weeks postpartum were correlated (r = 0.47, p < 0.001, n = 596). Among women consuming drinking water Mn in the highest tertile (i.e., > 9.8 μg/L) significant positive correlations were found between water Mn and toenails Mn (r = 0.31 and r = 0.38, for toenail samples collected during pregnancy and postpartum, respectively), whereas little to no correlation was observed at lower water concentrations. Overall, our data suggest that maternal toenail samples are a reliable environmental Mn exposure biomarker and reflect exposure from drinking water.

Manganese exposure and working memory-related brain activity in smallholder farmworkers in Costa Rica: Results from a pilot study

Main sources of manganese (Mn) in the general population are diet and drinking water. Mn is also found in ethylene bisdithiocarbamate (EBDC) fungicides used in agriculture or emitted into the air by ferromanganese plants and welding fumes, which can be additional environmental and occupational sources of exposure. High occupational Mn exposure has been linked with motor, behavioral, and cognitive impairment, but its effects on neural function remain poorly understood. We conducted a functional neuroimaging study in a sample of 48 farmworkers in Zarcero County, Costa Rica, an agricultural region where EBDC fungicides are sprayed. We measured Mn concentrations in farmworkers' toenails (n = 40 farmworkers) and hair (n = 33 farmworkers), and recorded brain activity in the dorsolateral prefrontal cortex during a letter-retrieval working memory task using functional near-infrared spectroscopy (fNIRS). We estimated exposure-outcome associations using multivariable linear regression models adjusted for age and education level. Geometric mean (geometric standard deviation) toenail and hair Mn concentrations were 0.40 μg/g (3.52) and 0.24 μg/g (3.54), respectively. We did not find strong evidence that Mn concentrations were associated with working memory-related brain activity in this sample of farmworkers; we also found null associations between working memory task accuracy and brain activity. However, our small sample size may have limited our ability to detect small effect sizes with statistical precision. Our study demonstrates that fNIRS can be a useful and feasible tool in environmental epidemiology for examining the effects of toxicants, like Mn, on neural function. This may prove to be important for elucidating neuropathological pathways that underlie previously reported associations of elevated Mn exposure with neurotoxic effects.

PET imaging of dopamine release in the frontal cortex of manganese-exposed non-human primates

Humans and non-human primates exposed to excess levels of manganese (Mn) exhibit deficits in working memory and attention. Frontal cortex and fronto-striatal networks are implicated in working memory and these circuits rely on dopamine for optimal performance. Here, we aimed to determine if chronic Mn exposure alters in vivo dopamine release (DAR) in the frontal cortex of non-human primates. We used [¹¹ C]-FLB457 positron emission tomography with amphetamine challenge to measure DAR in Cynomolgus macaques. Animals received [¹¹ C]-FLB457 positron emission tomography scans with and without amphetamine challenge prior to Mn exposure (baseline), at different time points during the Mn exposure period, and after 10 months of Mn exposure cessation. Four of six Mn-exposed animals expressed significant impairment of frontal cortex in vivo DAR relative to baseline. One Mn animal had no change in DAR and another Mn animal expressed increased DAR relative to baseline. In the reversal studies, one Mn-exposed animal exhibited complete recovery of DAR while the second animal had partial recovery. In both animals, frontal cortex Mn concentrations normalized after 10 months of exposure cessation based on T1-weighted magnetic resonance imaging. D1-dopamine receptor (D1R) autoradiography in frontal cortex tissue indicates that Mn animals that experienced cessation of Mn exposure expressed D1R levels that were approximately 50% lower than Mn animals that did not experience cessation of Mn exposure or control animals. The present study provides evidence of Mn-induced alterations in frontal cortex DAR and D1R that may be associated with working memory and attention deficits observed in Mn-exposed subjects.

Iron and manganese-related CNS toxicity: mechanisms, diagnosis and treatment

INTRODUCTION

Iron (Fe) and manganese (Mn) are essential nutrients for humans. They act as cofactors for a variety of enzymes. In the central nervous system (CNS), these two metals are involved in diverse neurological activities. Dyshomeostasis may interfere with the critical enzymatic activities, hence altering the neurophysiological status and resulting in neurological diseases. Areas covered: In this review, the authors cover the molecular mechanisms of Fe/Mn-induced toxicity and neurological diseases, as well as the diagnosis and potential treatment. Given that both Fe and Mn are abundant in the earth crust, nutritional deficiency is rare. In this review the authors focus on the neurological disorders associated with Mn and Fe overload. Expert commentary: Oxidative stress and mitochondrial dysfunction are the primary molecular mechanism that mediates Fe/Mn-induced neurotoxicity. Although increased Fe or Mn concentrations have been found in brain of patients, it remains controversial whether the elevated metal amounts are the primary cause or secondary consequence of neurological diseases. Currently, treatments are far from satisfactory, although chelation therapy can significantly decrease brain Fe and Mn levels. Studies to determine the primary cause and establish the molecular mechanism of toxicity may help to adapt more comprehensive and satisfactory treatments in the future.

The reproducibility of urinary ions in manganese exposed workers

PURPOSE

Manganese (Mn) is found in environmental and occupational settings, and can cause cognitive and motor impairment. Existing Mn exposure studies have not reached consensus on a valid and reproducible biomarker for Mn exposure.

METHODS

Previously, global metabolomics data was generated from urine collected in October 2014 using mass spectrometry (MS). Nine ions were found to be different between persons exposed and unexposed to Mn occupationally, though their identity was not able to be determined. Here, we investigated these nine ions in a follow-up set of urine samples taken from the same cohort in January 2015, and in urine samples from a separate Mn-exposed cohort from Wisconsin. We fit an elastic net model fit using the nine ions found in the October 2014 data.

RESULTS

The elastic net correctly predicted exposure status in 72% of the follow-up samples collected in January 2015, and the area under the curve of the receiver operating characteristic (ROC) curve was 0.8. In the Wisconsin samples, the elastic net performed no better than chance in predicting exposure, possibly due to differences in Mn exposure levels, or unmeasured occupational or environmental co-exposures.

CONCLUSIONS

This work underscores the importance of taking repeat samples for replication studies when investigating the human urine metabolome, as both within- and between-person variances were observed. Validating and identifying promising results remains a challenge in harnessing global metabolomics for biomarker discovery in occupational cohorts.

Ethanol exacerbates manganese - induced functional alterations along the hypothalamic-pituitary-gonadal axis of male rats

Manganese (Mn) exposure has been reported to induce reproductive dysfunction in animal and humans. Studies have shown that a large percentage of adolescent and adult populations tend to consume alcohol in a binge pattern. However, there is no information on the influence of alcohol on Mn - induced functional alteration along the hypothalamic - pituitary - gonadal axis. This study aimed to evaluate the influence of ethanol (EtOH) on Mn - induced functional alteration along the hypothalamic - pituitary - gonadal axis. Rats were exposed to Mn alone at 30 mg/kg body weight or co-expose with EtOH at 1.25 and 5 g/kg body weight for 35 consecutive days. Results showed that EtOH exposure significantly (p ≤ 0.05) exacerbated Mn - induced decrease in antioxidant enzymes activities, glutathione level and increased oxidative stress biomarkers in the hypothalamus, testes an epididymis of the exposed rats. Moreover, induction of inflammation was associated with disruption of histo-architecture of the hypothalamus, testes and epididymis of rats treated with Mn alone, EtOH alone or in combination. Furthermore, EtOH significantly exacerbated Mn - induced diminution in reproductive hormones and marker enzymes of testicular functions coupled with decreased sperm quantity and quality. Taken together, EtOH exacerbates Mn - induced functional alteration along the hypothalamic - pituitary - gonadal axis in rats via mechanisms involving induction of oxidative/nitrosative stress, lipid peroxidation and inflammation in rats.

Manganese and neurobehavioral impairment. A preliminary risk assessment

Similar patterns of cognitive and motor deficits have been widely reported from manganese exposures in welding, metallurgical and chemical industry workers. A risk assessment was performed based on studies reported in the literature, extending some earlier work, and deriving new estimates of exposure response and excess risk. Many investigations of manganese neurological effects in humans have insufficient information to derive an exposure response; however, findings from a chemical manufacturer, two smelter and two welder populations permitted application of the benchmark dose procedure for continuous end-points. Small particles and aggregates of condensation fume (condensing vaporized metal, <0.1μm in diameter) appear to have a higher potency per unit mass than larger particles from dusts (>1.0μm). Consideration was given to long-term effects of continuous low exposures that instead of producing increasing toxicity attain a steady-state condition. Impairment was defined as excursions beyond the 5th percentile in a normal population and the concentrations of manganese predicted to result in 1% excess prevalence of impairment over different time periods were calculated. Over five years, exposures resulting in 1% excess prevalence of impairment (for purposes of discussion) were in the vicinity of 10μg/m³ for manganese fume and 25μg/m³ for larger particle dusts. These levels are below current recommendations for occupational limits on manganese exposure in the United States.

The Use of Metabolomics to Identify Biological Signatures of Manganese Exposure

Objectives

Manganese (Mn) is a known neurotoxicant, and given its health effects and ubiquitous nature in metal-working settings, identification of a valid and reproducible biomarker of Mn exposure is of interest. Here, global metabolomics is utilized to determine metabolites that differ between groups defined by Mn exposure status, with the goal being to help inform a potential metabolite biomarker of Mn exposure.

Methods

Mn exposed subjects were recruited from a Mn steel foundry and Mn unexposed subjects were recruited from crane operators at a metal recycling facility. Over the course of a work day, each subject wore a personal inhalable dust sampler (IOM), and provided an end of shift urine sample that underwent global metabolomics profiling. Both exposed and unexposed subjects were divided into a training set and demographically similar validation set. Using a two-sided adjusted t-test, relative abundances of all metabolites found were compared between Mn exposed and unexposed training sets, and those with a false discovery rates (FDR) <0.1 were further tested in the validation sets.

Results

Fifteen ions were found to be significantly different (FDR < 0.1) between the exposed and unexposed training sets, and nine of these ions remained significantly different between the exposed and unexposed validation set as well. When further dividing exposure status into 'lower exposure' and 'higher exposure', several of these nine ions exhibited an apparent exposure-response relationship.

Conclusions

This is the first time that metabolomics has been used to distinguish between Mn exposure status in an occupational cohort, though additional work should be done to replicate these findings with a larger cohort. With metabolite identification by name, empirical formula, or pathway, a better understanding of the relationship between Mn exposure and neurotoxic effects could be elucidated, and a potential metabolite biomarker of Mn exposure could be determined.

A tissue dose-based comparative exposure assessment of manganese using physiologically based pharmacokinetic modeling-The importance of homeostatic control for an essential metal

A physiologically-based pharmacokinetic (PBPK) model (Schroeter et al., 2011) was applied to simulate target tissue manganese (Mn) concentrations following occupational and environmental exposures. These estimates of target tissue Mn concentrations were compared to determine margins of safety (MOS) and to evaluate the biological relevance of applying safety factors to derive acceptable Mn air concentrations. Mn blood concentrations measured in occupational studies permitted verification of the human PBPK models, increasing confidence in the resulting estimates. Mn exposure was determined based on measured ambient air Mn concentrations and dietary data in Canada and the United States (US). Incorporating dietary and inhalation exposures into the models indicated that increases in target tissue concentrations above endogenous levels only begin to occur when humans are exposed to levels of Mn in ambient air (i.e. >10μg/m³) that are far higher than those currently measured in Canada or the US. A MOS greater than three orders of magnitude was observed, indicating that current Mn air concentrations are far below concentrations that would be required to produce the target tissue Mn concentrations associated with subclinical neurological effects. This application of PBPK modeling for an essential element clearly demonstrates that the conventional application of default factors to "convert" an occupational exposure to an equivalent continuous environmental exposure, followed by the application of safety factors, is not appropriate in the case of Mn. PBPK modeling demonstrates that the relationship between ambient Mn exposures and dose-to-target tissue is not linear due to normal tissue background levels and homeostatic controls.

Effects of manganese exposure on visuoperception and visual memory in schoolchildren

BACKGROUND

Manganese (Mn) is an essential metal involved in multiple physiological functions. Environmental exposure to airborne Mn is associated with neurocognitive deficits in humans. Children, whose nervous system is in development, are particularly susceptible to Mn neurotoxicity.

OBJECTIVE

The objective of this study was to assess the association between Mn environmental exposure, and effects on visuoperception and visual memory in schoolchildren.

METHODS

We assessed schoolchildren between 7 and 11 years old, with similar socioeconomic status, from the mining district of Molango (n=148) and Agua Blanca (n=119, non-mining area) in Hidalgo state, Mexico. The Rey-Osterrieth Complex Figure (ROCF) test was used to assess visuoperception and short-term visual memory. Hair manganese (MnH) concentrations were determined. Linear regression models were constructed to estimate the associations between MnH and ROCF scores, adjusted for potential confounders.

RESULTS

The geometric mean MnH was nine times higher in schoolchildren from the Mn mining area (5.25μg/g) than in schoolchildren from the non-mining area (0.55μg/g). For the ROCF Copy trial, MnH was significantly associated with an increase in distortion errors (tangency, closure), angle errors, overtracing (partial overtracing). In the Immediate Recall trial, MnH was significantly associated with increased overtracing (partial overtracing) and omissions, and negatively associated with the number of perceptual drawn units, total score and percentage immediate recall.

CONCLUSIONS

MnH is associated with alterations in visuoperception and short-term visual memory in schoolchildren exposed to airborne Mn.

Setting evidence-based occupational exposure limits for manganese

In 2004, a review by the Institute of Environment and Health (IEH) made recommendations on occupational exposure limits (OELs) for manganese and its inorganic compounds for inhalable and respirable fractions respectively. These OELs were based on a detailed comprehensive evaluation of all the scientific data available at that time. Since then, more published studies have become available and a number of occupational standard-setting committees (EU SCOEL, US ACGIH-TLV, and German MAK) have proposed OEL's for manganese and its inorganic compounds that are somewhat lower that those proposed in the 2004 review. Based on current understanding, the key toxicological and human health issues that are likely to influence a health-based recommendation relate to: neurotoxicology; reproductive and developmental toxicology; and mutagenicity/carcinogenicity. Of these, it is generally considered that neurotoxicity presents the most sensitive endpoint. As such, many of the studies that have been reported since the IEH review have sought to use those neurofunctional tests that appear to be particularly sensitive at identifying the subtle neurological changes thought to associate with manganese toxicity. These recent studies have, however, continued to be limited to a significant extent by reliance on cross-sectional designs and also by use of unreliable exposure estimation methods. Consequently the strength of the potential association between manganese exposure and these subtle subclinical cognitive or neuromotor changes is still poorly characterised and the relevance of these minor differences in terms of either their clinical or quality of life consequences remains unknown. Based upon the overall evidence, it is concluded that the 8-h time weighted averages (TWA) for respirable (0.05mg/m³ as Mn) and inhalable (0.2mg/m³ as Mn) fractions as recommended by the SCOEL in 2011 are the most methodologically-sound, as they are based on the best available studies, most suited to the development of health-based OELs for both respirable and inhalable fractions. The dose-response characterisation informed by the examined studies used can be considered to establish a true human NOAEL for all the neurofunctional endpoints examined within the selected studies.

Relations of biomarkers of manganese exposure and neuropsychological effects among welders and ferroalloy smelters

The objective of present study was to assess relationship between biomarkers of Manganese (Mn) and neuropsychological effects. The study was carried out on 27 welders and 31 ferroalloy smelters as Mn-exposed groups and 30 office workers as unexposed controls. Air Mn concentrations were determined according to NIOSH method 7300. The biological samples were prepared using microwave assisted acid digestion and all samples were analyzed by graphite furnace- atomic absorption spectroscopy (GF-AAS) in order to determine manganese. Questionnaire 16 (Q16) and Cambridge Neuropsychological Test Automated Battery (CANTAB) were used to evaluate the neuropsychological effects. The mean concentrations of air Mn for the welder and ferroalloy smelter groups were 0.023 ± 0.012 mg/m(3) and 0.008 ± 0.005 mg/m(3), respectively. Manganese concentrations in blood, urine, and toenail samples of exposed workers ranged between 1.80-32.60 (µg/l), 1.00-42.50 (µg/l), and 0.10-6.08 (µg/g), respectively. Mean Mn concentrations in all biological samples of cases were significantly higher than unexposed controls (p<0.05). A moderate relationship was observed between biomarkers of Mn exposure, air Mn, Q16 as well as some neurocognitive outcome measures. The present study shows that blood Mn, urine Mn and toenail Mn could be used to distinguish Mn-exposed workers from unexposed population at the group level.

A Dosimetry Study of Deuterium-Deuterium Neutron Generator-based In Vivo Neutron Activation Analysis

A neutron irradiation cavity for in vivo neutron activation analysis (IVNAA) to detect manganese, aluminum, and other potentially toxic elements in human hand bone has been designed and its dosimetric specifications measured. The neutron source is a customized deuterium-deuterium neutron generator that produces neutrons at 2.45 MeV by the fusion reaction 2H(d, n)3He at a calculated flux of 7 × 10(8) ± 30% s(-1). A moderator/reflector/shielding [5 cm high density polyethylene (HDPE), 5.3 cm graphite and 5.7 cm borated (HDPE)] assembly has been designed and built to maximize the thermal neutron flux inside the hand irradiation cavity and to reduce the extremity dose and effective dose to the human subject. Lead sheets are used to attenuate bremsstrahlung x rays and activation gammas. A Monte Carlo simulation (MCNP6) was used to model the system and calculate extremity dose. The extremity dose was measured with neutron and photon sensitive film badges and Fuji electronic pocket dosimeters (EPD). The neutron ambient dose outside the shielding was measured by Fuji NSN3, and the photon dose was measured by a Bicron MicroREM scintillator. Neutron extremity dose was calculated to be 32.3 mSv using MCNP6 simulations given a 10-min IVNAA measurement of manganese. Measurements by EPD and film badge indicate hand dose to be 31.7 ± 0.8 mSv for neutrons and 4.2 ± 0.2 mSv for photons for 10 min; whole body effective dose was calculated conservatively to be 0.052 mSv. Experimental values closely match values obtained from MCNP6 simulations. These are acceptable doses to apply the technology for a manganese toxicity study in a human population.

Developmental exposure to manganese induces lasting motor and cognitive impairment in rats

Exposure to high manganese (Mn) levels may damage the basal ganglia, leading to a syndrome analogous to Parkinson's disease, with motor and cognitive impairments. The molecular mechanisms underlying Mn neurotoxicity, particularly during development, still deserve further investigation. Herein, we addressed whether early-life Mn exposure affects motor coordination and cognitive function in adulthood and potential underlying mechanisms. Male Wistar rats were exposed intraperitoneally to saline (control) or MnCl2 (5, 10 or 20 mg/kg/day) from post-natal day (PND) 8-12. Behavioral tests were performed on PND 60-65 and biochemical analysis in the striatum and hippocampus were performed on PND14 or PND70. Rats exposed to Mn (10 and 20 mg/kg) performed significantly worse on the rotarod test than controls indicating motor coordination and balance impairments. The object and social recognition tasks were used to evaluate short-term memory. Rats exposed to the highest Mn dose failed to recognize a familiar object when replaced by a novel object as well as to recognize a familiar juvenile rat after a short period of time. However, Mn did not alter olfactory discrimination ability. In addition, Mn-treated rats displayed decreased levels of non-protein thiols (e.g. glutathione) and increased levels of glial fibrillary acidic protein (GFAP) in the striatum. Moreover, Mn significantly increased hippocampal glutathione peroxidase (GPx) activity. These findings demonstrate that acute low-level exposure to Mn during a critical neurodevelopmental period causes cognitive and motor dysfunctions that last into adulthood, that are accompanied by alterations in antioxidant defense system in both the hippocampus and striatum.

Neuropsychologic evaluation and exposure to neurotoxicants

The history of neuropsychologic assessment describes the development of a psychometric approach to neuropsychologic measurement, based on the initial clinical/theoretical approach exemplified by pioneers, who also discussed different brain functions and hypotheses for clinical exploration and treatment. Early neuropsychologic assessment practices in the USA arose out of the need to screen, diagnose, and treat World War II veterans who returned with brain injuries. Clinical testing was used to determine treatment and rehabilitation potential. Clinical psychologists had previously developed educational tests to investigate students' abilities and disabilities. Using population studies, primarily in the USA, Canada and Europe, neuropsychologists developed standardized test scores, permitting comparisons of scores based on the normal curve and evolving knowledge of brain/behavior relationships. In clinical interpretations, neuropsychologists use extensive normative data based on cognitive, mood, executive, neurologic, and motor brain functions of groups with different cultural and educational backgrounds and psychiatric illnesses. Large groups of workers can be screened with a brief neuropsychologic screening test battery to assess the psychologic status of personnel. Commonly used tests by domain are described, as well as patterns of acute and chronic neurotoxicant exposures, treatment, and rehabilitation. Future developments will relate imaging studies to neuropsychologic performance.

Reconsideration of the WHO NCTB strategy and test selection

The World Health Organization-recommended neurobehavioral core test battery (NCTB) became the international standard for identifying adverse human behavioral effects due to neurotoxic chemical exposure when it was first proposed in 1983. Since then the WHO NCTB has been repeatedly cited as the basis for test selection in human neurotoxicology research. A discussion group was held before the International Symposium on Neurobehavioral Methods and Effects in Occupational and Environmental Health to review the NCTB and reconsider its tests. The workshop made three consensus recommendations to the International Congress on Occupational Health (ICOH) Scientific Committee on Neurotoxicology and Psychophysiology (SCNP):. 1. A 'screening' battery of broadly sensitive tests is needed as guidance to the field of human neurotoxicology 2. The SCNP should convene a panel to reconsider the functions measured and the tests in the WHO NCTB 3. Three disciplines should be represented in the panel recommending a revised NCTB: neuropsychology; experimental psychology; neurology. This recommendation will be pursued at the next meeting of the International Congress on Occupational Health (ICOH) Scientific Committee on Neurotoxicology and Psychophysiology (SCNP).

Manganese leads to an increase in markers of oxidative stress as well as to a shift in the ratio of Fe(II)/(III) in rat brain tissue

Occupationally or environmentally caused chronic exposure to Manganese (Mn) can lead to a degeneration of dopaminergic neurons inducing a Parkinson-like complaint called manganism. Deciphering the ongoing neurodegenerative mechanisms in the affected brain is still a major task for understanding the complex modes of action. Therefore, we applied a non-toxic, oral feeding in rats simulating a chronic exposure to Mn. Analysis of brain extracts by electrospray ionization Fourier transform resonance mass spectrometry (ESI-FT-ICR-MS) revealed an increase in markers of oxidative stress like glutathione disulfide (GSSG), prostaglandins, and 15(S)-HETE, a marker of lipid peroxidation. Furthermore, acetylcholinesterase (AchE) activity and glutamate concentrations were elevated in brain samples of Mn-supplemented rats, suggesting oxidative stress in the brain tissue. Application of ion chromatography coupled to inductively coupled plasma-optical emission spectrometry (IC-ICP-OES) further showed a shift of Fe(III) towards Fe(II) in the brain samples enabling for example the action of the Fenton reaction. This is the first time that changes in the Fe-species distribution could be related to Mn-induced neuroinflammation and is therefore enlarging the knowledge of this complex neurodegenerative condition. The combination of our findings provides substantial evidence that Mn-induced neuroinflammation leads to oxidative stress triggered by multifactorial pathophysiological processes.

Manganese-induced atypical parkinsonism is associated with altered Basal Ganglia activity and changes in tissue levels of monoamines in the rat

Manganese neurotoxicity is associated with motor and cognitive disturbances known as Manganism. However, the mechanisms underlying these deficits remain unknown. Here we investigated the effects of manganese intoxication on motor and non-motor parkinsonian-like deficits such as locomotor activity, motor coordination, anxiety and “depressive-like” behaviors. Then, we studied the impact of this intoxication on the neuronal activity, the globus pallidus (GP) and subthalamic nucleus (STN). At the end of experiments, post-mortem tissue level of the three monoamines (dopamine, norepinephrine and serotonin) has been determined. The experiments were carried out in adult Sprague-Dawley rats, daily treated with MnCl₂ (10 mg/kg/, i.p.) for 5 weeks. We show that manganese progressively reduced locomotor activity as well as motor coordination in parallel with the manifestation of anxiety and “depressive-like” behaviors. Electrophysiological results show that, while majority of GP and STN neurons discharged regularly in controls, manganese increased the number of GP and STN neurons discharging irregularly and/or with bursts. Biochemical results show that manganese significantly decreased tissue levels of norepinephrine and serotonin with increased metabolism of dopamine in the striatum. Our data provide evidence that manganese intoxication is associated with impaired neurotransmission of monoaminergic systems, which is at the origin of changes in basal ganglia neuronal activity and the manifestation of motor and non-motor deficits similar to those observed in atypical Parkinsonism.

Airborne manganese as dust vs. fume determining blood levels in workers at a manganese alloy production plant

The appropriate exposure metrics for characterizing manganese (Mn) exposure associated with neurobehavioral effects have not been established. Blood levels of Mn (B-Mn) provide a potentially important intermediate marker of Mn airborne exposures. Using data from a study of a population of silicon- and ferro-manganese alloy production workers employed between 1973 and 1991, B-Mn levels were modeled in relation to prior Mn exposure using detailed work histories and estimated respirable Mn concentrations from air-sampling records. Despite wide variation in exposure levels estimated for individual jobs, duration of employment (exposure) was itself a strong predictor of B-Mn levels and strongest when an 80-day half-life was applied to contributions over time (t=6.95, 7.44, respectively; p<10(-5)). Partitioning exposure concentrations based on process origin into two categories: (1) "large" respirable particulate (Mn-LRP) derived mainly from mechanically generated dust, and (2) "small" respirable particulate (Mn-SRP) primarily electric furnace condensation fume, revealed that B-Mn levels largely track the small, fume exposures. With a half-life of 65 days applied in a model with cumulative exposure terms for both Mn-LRP (t=-0.16, p=0.87) and Mn-SRP (t=6.45, p<10(-5)), the contribution of the large-size fraction contribution was negligible. Constructing metrics based on the square root of SRP exposure concentrations produced a better model fit (t=7.87 vs. 7.44, R(2)=0.2333 vs. 0.2157). In a model containing both duration (t=0.79, p=0.43) and (square root) fume (t=2.47, p=0.01) metrics, the duration term was a weak contributor. Furnace-derived, small respirable Mn particulate appears to be the primary contributor to B-Mn levels, with a dose-rate dependence in a population chronically exposed to Mn, with air-concentrations declining in recent years. These observations may reflect the presence of homeostatic control of Mn levels in the blood and other body tissues and be useful in assessing Mn exposures for evaluating neurotoxic effects.

New insights into manganese toxicity and speciation

Manganese (Mn) is known to be a neurotoxic agent for nearly 175 years now. A lot of research has therefore been carried out over the last century. From preliminary describing only symptoms of Mn-(over)exposed workers, research was preceded to more detail on toxic mechanisms of Mn. Unraveling those neurotoxic mechanisms implicated a number of studies, which were summarized partly in several reviews (e.g. Yokel RA. Neuromol Med 2009;11(4):297-310; Aschner M, et al. Toxicology Appl Pharmacol 2007;221(2):131-47; Michalke B, et al. J Environ Monit 2007;9(7):650). Since our recent review on Mn-speciation in 2007 (Michalke B, et al. J Environ Monit 2007;9(7):650), Mn-research was considerably pushed forward and several new research articles were published. The very recent years though, Mn toxicity investigating science is spreading into different fields with very detailed and complex study designs. Especially the mechanisms of Mn-induced neuronal injury on cellular and molecular level was investigated in more detail, discussing neurotransmitter and enzyme interactions, mechanisms of action on DNA level and even inclusion of genetic influences. Depicting the particular Mn-species was also a big issue to determine which molecule is transporting Mn at the cell membranes and which one is responsible for the injury of neuronal tissue. Other special foci on epidemiologic studies were becoming more and more important: These foci were directed toward environmental influences of Mn on especially Parkinson disease prevalence and the ability to carry out follow-up studies about Mn-life-span exposure. All these very far-reaching research applications may finally lead to a suitable future human Mn-biomonitoring for being able to prevent or at least detect the early onset of manganism at the right time.

Manganese neurotoxicity: new perspectives from behavioral, neuroimaging, and neuropathological studies in humans and non-human primates

Manganese (Mn) is an essential metal and has important physiological functions for human health. However, exposure to excess levels of Mn in occupational settings or from environmental sources has been associated with a neurological syndrome comprising cognitive deficits, neuropsychological abnormalities and parkinsonism. Historically, studies on the effects of Mn in humans and experimental animals have been concerned with effects on the basal ganglia and the dopaminergic system as it relates to movement abnormalities. However, emerging studies are beginning to provide significant evidence of Mn effects on cortical structures and cognitive function at lower levels than previously recognized. This review advances new knowledge of putative mechanisms by which exposure to excess levels of Mn alters neurobiological systems and produces neurological deficits not only in the basal ganglia but also in the cerebral cortex. The emerging evidence suggests that working memory is significantly affected by chronic Mn exposure and this may be mediated by alterations in brain structures associated with the working memory network including the caudate nucleus in the striatum, frontal cortex and parietal cortex. Dysregulation of the dopaminergic system may play an important role in both the movement abnormalities as well as the neuropsychiatric and cognitive function deficits that have been described in humans and non-human primates exposed to Mn.

Neuropsychiatric symptom assessments in toxic exposure

The goal of this review is to provide guidelines for evaluating psychiatric and mood changes that result from neurotoxicity. Mood changes that are often seen to varying degrees in neurotoxicity include increased anxiety, depression, irritability, impulsiveness, and psychosis. Some common agents that induce neurotoxicity include drugs, heavy metals, and organophosphates with presentations varying somewhat depending upon the mechanism of toxicity. The authors discuss in detail psychiatric assessment for patients with suspected of having neurotoxicologic syndrome.

Lead exposure and fear-potentiated startle in the VA Normative Aging Study: a pilot study of a novel physiological approach to investigating neurotoxicant effects

BACKGROUND

Physiologically-based indicators of neural plasticity in humans could provide mechanistic insights into toxicant actions on learning in the brain, and perhaps prove more objective and sensitive measures of such effects than other methods.

OBJECTIVES

We explored the association between lead exposure and classical conditioning of the acoustic startle reflex (ASR)-a simple form of associative learning in the brain-in a population of elderly men. Fifty-one men from the VA Normative Aging Study with cumulative bone lead exposure measurements made with K-X-Ray-Fluorescence participated in a fear-conditioning protocol.

RESULTS

The mean age of the men was 75.5years (standard deviation [sd]=5.9) and mean patella lead concentration was 22.7μg/g bone (sd=15.9). Baseline ASR eyeblink response decreased with age, but was not associated with subsequent conditioning. Among 37 men with valid responses at the end of the protocol, higher patella lead was associated with decreased awareness of the conditioning contingency (declarative learning; adjusted odds ratio [OR] per 20μg/g patella lead=0.91, 95% confidence interval [CI]: 0.84, 0.99, p=0.03). Eyeblink conditioning (non-declarative learning) was 0.44sd less (95% CI: -0.91, 0.02; p=0.06) per 20μg/g patella lead after adjustment. Each result was stronger when correcting for the interval between lead measurement and startle testing (awareness: OR=0.88, 95% CI: 0.78, 0.99, p=0.04; conditioning: -0.79sd less, 95% CI: -1.56, 0.03, p=0.04).

CONCLUSIONS

This initial exploration suggests that lead exposure interferes with specific neural mechanisms of learning and offers the possibility that the ASR may provide a new approach to physiologically explore the effects of neurotoxicant exposures on neural mechanisms of learning in humans with a paradigm that is directly comparable to animal models.

Levels and predictors of airborne and internal exposure to manganese and iron among welders

We investigated airborne and internal exposure to manganese (Mn) and iron (Fe) among welders. Personal sampling of welding fumes was carried out in 241 welders during a shift. Metals were determined by inductively coupled plasma mass spectrometry. Mn in blood (MnB) was analyzed by graphite furnace atom absorption spectrometry. Determinants of exposure levels were estimated with multiple regression models. Respirable Mn was measured with a median of 62 (inter-quartile range (IQR) 8.4-320) μg/m(3) and correlated with Fe (r=0.92, 95% CI 0.90-0.94). Inhalable Mn was measured with similar concentrations (IQR 10-340 μg/m(3)). About 70% of the variance of Mn and Fe could be explained, mainly by the welding process. Ventilation decreased exposure to Fe and Mn significantly. Median concentrations of MnB and serum ferritin (SF) were 10.30 μg/l (IQR 8.33-13.15 μg/l) and 131 μg/l (IQR 76-240 μg/l), respectively. Few welders were presented with low iron stores, and MnB and SF were not correlated (r=0.07, 95% CI -0.05 to 0.20). Regression models revealed a significant association of the parent metal with MnB and SF, but a low fraction of variance was explained by exposure-related factors. Mn is mainly respirable in welding fumes. Airborne Mn and Fe influenced MnB and SF, respectively, in welders. This indicates an effect on the biological regulation of both metals. Mn and Fe were strongly correlated, whereas MnB and SF were not, likely due to higher iron stores among welders.

Environmental exposure to manganese and motor function of children in Mexico

OBJECTIVES

Occupational manganese (Mn) exposure has been associated with motor deficits in adult workers, but data on the potential effects of environmental exposure to Mn on the developing motor function for a children population is scarce. The aim of this study was to evaluate the association between exposure to Mn and motor function of school aged children.

METHODS

We conducted a cross-sectional study selecting 195 children (100 exposed and 95 unexposed) between 7 and 11 years old. The following tests were used to evaluate the motor function: Grooved pegboard, finger tapping, and Santa Ana test. Mn exposure was assessed by blood (MnB) and hair concentrations (MnH). We constructed linear regression models to evaluate the association between exposure to Mn and the different test scores adjusting for age, sex, maternal education, hemoglobin and blood lead.

RESULTS

The median concentration of MnH and MnB was significantly higher in exposed (12.6 μg/g and 9.5 μg/L) compared to unexposed children (0.6 μg/g and 8.0 μg/L). The exposed children on average performed the grooved pegboard test faster, but made more errors, although these results did not reach statistical significance with neither one of the Mn exposure biomarkers. MnB showed an inverse association on the execution of the finger tapping test (average in 5 trials β -0.4, p=0.02), but no association was observed with MnH.

CONCLUSIONS

A subtle negative association of Mn exposure on motor speed and coordination was shown. In adults, the main effect of environmental Mn exposure has been associated with motor skills, but these results suggest that such alterations are not the main effect on children.

Manganese-induced NF-kappaB activation and nitrosative stress is decreased by estrogen in juvenile mice

Manganese toxicity can cause a neurodegenerative disorder affecting cortical and basal ganglia structures with a neurological presentation resembling features of Parkinson's disease. Children are more sensitive to Mn-induced neurological dysfunction than adults, and recent studies from our laboratory revealed a marked sensitivity of male juvenile mice to neuroinflammatory injury from Mn, relative to females. To determine the role of estrogen (E2) in mediating sex-dependent vulnerability to Mn-induced neurotoxicity, we exposed transgenic mice expressing an NF-κB-driven enhanced green fluorescent protein (EGFP) reporter construct (NF-κB-EGFP mice) to Mn, postulating that supplementing male mice with E2 during juvenile development would attenuate neuroinflammatory changes associated with glial activation, including expression of inducible nitric oxide synthase (NOS2) and neuronal protein nitration. Juvenile NF-κB-EGFP mice were separated in groups composed of females, males, and males surgically implanted with Silastic capsules containing 25 μg of 17-β-estradiol (E2) or vehicle control. Mice were then treated with 0 or 100 mg/Kg MnCl(2) by intragastric gavage from postnatal days 21-34. Manganese treatment caused alterations in levels of striatal dopamine, as well as increases in NF-κB reporter activity and NOS2 expression in both microglia and astrocytes that were prevented by supplementation with E2. E2 also decreased neuronal protein nitration in Mn-treated mice and inhibited apoptosis in striatal neurons cocultured with Mn-treated astrocytes in vitro. These data indicate that E2 protects against Mn-induced neuroinflammation in developing mice and that NF-κB is an important regulator of neuroinflammatory gene expression in glia associated with nitrosative stress in the basal ganglia during Mn exposure.

Manganese and acute paranoid psychosis: a case report

Introduction

Manganese regulates many enzymes and is essential for normal development and body function. Chronic manganese intoxication has an insidious and progressive course and usually starts with complaints of headache, fatigue, sleep disturbances, irritability and emotional instability. Later, several organ systems may be affected and, due to neurotoxicity, an atypical parkinsonian syndrome may emerge. With regard to neuropsychiatry, an array of symptoms may develop up to 30 years after intoxication, of which gait and speech abnormalities, cognitive and motor slowing, mood changes and hallucinations are the most common. Psychotic phenomena are rarely reported.

Case presentation

We describe the case of a 49-year-old Caucasian man working as a welder who was referred to our facility for evaluation of acute paranoid psychotic behavior. Our patient's medical history made no mention of any somatic complaints or psychiatric symptoms, and he had been involved in a professional career as a metalworker. On magnetic resonance imaging scanning of his brain, a bilateral hyperdensity of the globus pallidus, suggestive for manganese intoxication, was found. His manganese serum level was 52 to 97 nmol/L (range: 7 to 20 nmol/L). A diagnosis of organic psychotic disorder due to manganese overexposure was made. His psychotic symptoms disappeared within two weeks of treatment with low-dose risperidone. At three months later, serum manganese was decreased to slightly elevated levels and the magnetic resonance imaging T1 signal intensity was reduced. No signs of Parkinsonism were found and a definite diagnosis of manganese-induced apathy syndrome was made.

Conclusion

Although neuropsychiatric and neurological symptoms caused by (chronic) manganese exposure have been reported frequently in the past, in the present day the disorder is rarely diagnosed. In this report we stress that manganese intoxication can still occur, in our case in a confined-space welder, and may present clinically with a paranoid psychotic state that necessitates a rapid diagnostic procedure in order to avoid the permanent structural brain damage that may occur with chronic exposure.

Proposal for a revised Reference Concentration (RfC) for manganese based on recent epidemiological studies

In 1993, based on observations of subclinical neurological effects in workers, the United States Environmental Protection Agency (US EPA) published a Reference Concentration (RfC) of 0.05 microg/m(3) for manganese (Mn). The geometric mean exposure concentration, 150 microg/m(3) respirable Mn, was considered the lowest observable adverse effect level (LOAEL), and uncertainty factors (UFs) were applied to account for sensitive populations, database limitations, a LOAEL, subchronic exposure, and potential differences in toxicity of different forms of Mn. Based on a review of more recent literature, we propose two alternate Mn RfCs. Of 12 more recent occupational studies of eight cohorts with chronic exposure durations, examining subclinical neurobehavioral effects, predominantly on the motor system, three were considered appropriate for development of an RfC. All three studies yielded no observable adverse effect levels (NOAELs) of approximately 60 microg/m(3) respirable Mn. Converting the occupational NOAEL to a human equivalent concentration (HEC) of 21microg/m(3) (for continuous exposure) and applying a UF of 10 to account for intraspecies variability yielded an RfC of 2microg/m(3). We also derived a similar RfC (7 microg/m(3)) using an Mn benchmark dose (BMD) as the point of departure. Overall confidence in both RfCs is medium.

Manganese exposure among smelting workers: blood manganese-iron ratio as a novel tool for manganese exposure assessment

Unexposed control subjects (n = 106), power distributing and office workers (n = 122), and manganese (Mn)-exposed ferroalloy smelter workers (n = 95) were recruited to the control, low and high groups, respectively. Mn concentrations in saliva, plasma, erythrocytes, urine and hair were significantly higher in both exposure groups than in the controls. The Fe concentration in plasma and erythrocytes, however, was significantly lower in Mn-exposed workers than in controls. The airborne Mn levels were significantly associated with Mn/Fe ratio (MIR) of erythrocytes (eMIR) (r = 0.77, p < 0.01) and plasma (pMIR) (r = 0.70, p < 0.01). The results suggest that the MIR may serve as a useful biomarker to distinguish Mn-exposed workers from the unexposed, control population.

Manganese exposure among smelting workers: relationship between blood manganese-iron ratio and early onset neurobehavioral alterations

A biomarker for detection of early onset neurobehavioral alterations in manganism remains unknown. The purpose of this study was to use a neurobehavioral test battery to identify subtle changes in Mn-induced motor and memory dysfunction and to relate the quantifiable neurological dysfunction to an established Mn-exposure index such as blood manganese-iron ratio (MIR). A total of 323 subjects were recruited to control (n=106), low-exposure (122), and high-exposure (95) groups. The test battery consisted of standard testing procedures including the nine-hole and groove-type steadiness tester, Benton visual retention test, and Purdue pegboard coordination test. No significant health problems or clinically diagnosed neurological dysfunctions were observed. Benton test did not reveal any abnormal memory deficits among Mn-exposed smelters, nor did the groove and nine-hole tests detect any abnormality in dynamic and static steadiness in tested subjects. Purdue pegboard test showed a remarkable age-related decline in fine movement coordination among all study participants regardless of the Mn-exposure condition. Mn exposure significantly exacerbated this age-related deterioration. Statistical modeling revealed that the plasma and erythrocyte MIR (i.e., pMIR and eMIR, respectively) were associated with Purdue pegboard scores. Among all subjects whose MIR were above the cut-off value (COV), pMIR was significantly correlated with pegboard scores (r=-0.261, p=0.002), whereas for those subjects over the age of 40, the eMIR, but not pMIR, was associated with declined pegboard performance (r=-0.219, p=0.069). When both factors were taken into account (i.e., age>40 and MIR>the COV), only pMIR was inversely associated with pegboard scores. Combining their usefulness in Mn-exposure assessment, we recommend that the blood Mn-Fe ratio may serve as a reasonable biomarker not only for assessment of Mn exposure but also for health risk assessment.

Past occupational exposure to airborne manganese in a manganese alloy plant

A retrospective exposure assessment of a group of manganese (Mn) alloy workers was performed in conjunction with a 2004 follow-up study, 14 years after cessation of exposure, to evaluate the long-term effects of occupational Mn exposure on neurobehavioral functions. The ferro- and silico-Mn alloy plant opened in 1973 and closed in 1991. The airborne total Mn (TMn) exposures for job groupings were established using personal sampling data from a 1991 industrial hygiene survey. Historical short-term total dust (TDust) data were used to estimate past TDust exposure for job groupings and plant areas. Relationships between Mn content and TDust from the 1991 survey, supported by sparse historical data, were used to estimate TMn content in the historical TDust data. Results showed past personal TDust exposure levels much higher than those found in 1991. Changes in TDust levels and corresponding TMn levels were a function of changes in ventilation, work practices, and operations, not of product (ferro- or silico-Mn). Relationships between TMn and respirable Mn (RMn) from area sampling in 1991 were used to estimate RMn exposure for the job groups. Work histories for 112 workers were developed from payroll records, questionnaires, and interviews and combined with Mn exposure estimates to develop cumulative exposure indices (CEIs). The TMn CEI ranged from 0.27 mg/m(3)x years to 100.24 mg/m(3)x years, with an AM of 24.40 mg/m(3)x years and a GM of 14.06 mg/m(3)x years. The RMn CEI had an AM of 2.95 mg/m(3)x years and a GM of 1.78 mg/m(3)x years with a range of 0.05-12.03 mg/m(3)x years. Overall average TMn exposure intensity, the TMn CEI divided by time worked in years for each worker, had an AM of 1.6 mg Mn/m(3), a GM of 1.0 mg Mn/m(3), range 0.02-6.2 6 mg Mn/m(3). The results of the 2004 follow-up study showed several concentration-response relationships between TMn CEI and neurobehavioral outcomes, which suggest that increase in cumulative TMn exposure level has long-term consequences on the nervous system.

Manganese cumulative exposure and symptoms: a follow-up study of alloy workers

Long-term exposure to manganese (Mn) particulates through inhalation can be neurotoxic, with deficits in neuromotor and cognitive domains. Mn-exposed individuals also report symptoms, including fatigue, mood changes, irritability, concentration difficulties, and sweating in the absence of physical effort. The long-term course of Mn-related symptoms after cessation of exposure has never been examined. Male workers from a Mn-alloy production plant participated in a study on nervous system functions (initial examination), and were followed-up 14 years after plant closure. The relation between self-reported symptoms and Mn cumulative exposure index (CEI) was examined among 71 Mn-alloy workers and 71 referents. Symptoms from the questionnaire were grouped into categories, and the reported frequency was compared between referents and Mn-alloy workers in each Mn CEI tertile using General Linear Models, controlling for age, education, and alcohol consumption. A gradual increase in symptoms frequency was observed for complaints related to hearing and movement control both at initial and follow-up examination, and fatigue and autonomic nervous system only at initial examination. In addition, an exposure-effect relation was apparent for symptoms related to memory, concentration and balance reported at both examinations, with Mn-workers in the highest CEI tertile reporting the highest level of symptomatology. Sleeping complaints were not associated with exposure to Mn, while musculoskeletal pain and muscular weakness were reported more often by Mn-workers than referents but were not clearly related to CEI. The findings suggest that former Mn-alloy workers continue to perceive symptoms many years after cessation of exposure. Despite the limitations of self-reported symptoms, subjective complaints are an important part of a health assessment since they relate directly to perceived health status and day-to-day functioning.

Psychiatric issues in toxic exposures

Military, occupational, and environmental events can cause toxic injuries that require psychiatric diagnosis and treatment. This article reviews the psychiatric effects of neurotoxins, including nerve gases, ionizing radiation, insecticides, heavy metals, solvents, and other toxic agents. Diagnostic considerations and clinical tests for further evaluation of the numerous psychiatric conditions and symptoms caused by toxic exposures are discussed.

Manganese inhibits NMDA receptor channel function: implications to psychiatric and cognitive effects

Humans exposed to excess levels of manganese (Mn(2+)) express psychiatric problems and deficits in attention and learning and memory. However, there is a paucity of knowledge on molecular mechanisms by which Mn(2+) produces such effects. We now report that Mn(2+) is a potent inhibitor of [(3)H]-MK-801 binding to the NMDA receptor channel in rat neuronal membrane preparations. The inhibition of [(3)H]-MK-801 to the NMDA receptor channel by Mn(2+) was activity-dependent since Mn(2+) was a more potent inhibitor in the presence of the NMDA receptor co-agonists glutamate and glycine (K(i)=35.9+/-3.1 microM) than in their absence (K(i)=157.1+/-6.5 microM). We also show that Mn(2+) is a NMDA receptor channel blocker since its inhibition of [(3)H]-MK-801 binding to the NMDA receptor channel is competitive in nature. That is, Mn(2+) significantly increased the affinity constant (K(d)) with no significant effect on the maximal number of [(3)H]-MK-801 binding sites (B(max)). Under stimulating conditions, Mn(2+) was equipotent in inhibiting [(3)H]-MK-801 binding to NMDA receptors expressed in neuronal membrane preparations from different brain regions. However, under basal, non-stimulated conditions, Mn(2+) was more potent in inhibiting NMDA receptors in the cerebellum than other brain regions. We have previously shown that chronic Mn(2+) exposure in non-human primates increases Cu(2+), but not zinc or iron concentrations in the basal ganglia [Guilarte TR, Chen M-K, McGlothan JL, Verina T, Wong DF, Zhou Y, Alexander M, Rohde CA, Syversen T, Decamp E, Koser AJ, Fritz S, Gonczi H, Anderson DW, Schneider JS. Nigrostriatal dopamine system dysfunction and subtle motor deficits in manganese-exposed non-human primates. Exp Neurol 2006a;202:381-90]. Therefore, we also tested the inhibitory effects of Cu(2+) on [(3)H]-MK-801 binding to the NMDA receptor channel. The data shows that Cu(2+) in the presence of glutamate and glycine is a more potent inhibitor of the NMDA receptor than Mn(2+). Our findings suggest that the inhibitory effect of Mn(2+) and/or Cu(2+) on the NMDA receptor may produce a deficit in glutamatergic transmission in the brain of individuals exposed to excess levels of Mn(2+) and produce neurological dysfunction.